Population decline in a ground-nesting solitary squash bee (Eucera pruinosa) following exposure to a neonicotinoid insecticide treated crop (Cucurbita pepo)

Abstract

Insect pollinators are threatened by multiple environmental stressors, including pesticide exposure. Despite being important pollinators, solitary ground-nesting bees are inadequately represented by pesticide risk assessments reliant almost exclusively on honeybee ecotoxicology. Here we evaluate the effects of realistic exposure via squash crops treated with systemic insecticides (Admire-imidacloprid soil application, FarMore FI400-thiamethoxam seed-coating, or Coragen-chlorantraniliprole foliar spray) for a ground-nesting bee species (Hoary squash bee, Eucera pruinosa) in a 3-year semi-field experiment. Hoary squash bees provide essential pollination services to pumpkin and squash crops and commonly nest within cropping areas increasing their risk of pesticide exposure from soil, nectar, and pollen. When exposed to a crop treated at planting with soil-applied imidacloprid, these bees initiated 85% fewer nests, left 5.3 times more pollen unharvested, and produced 89% fewer offspring than untreated controls. No measurable impacts on bees from exposure to squash treated with thiamethoxam as a seed-coating or foliage sprayed with chlorantraniliprole were found. Our results demonstrate important sublethal effects of field-realistic exposure to a soil-applied neonicotinoid (imidacloprid) on bee behaviour and reproductive success. Soil must be considered a potential route of pesticide exposure in risk assessments, and restrictions on soil-applied insecticides may be justified, to mitigate impacts on ground-nesting solitary bee populations and the crop pollination services they provide.

A systematic scoping review of the methodological approaches and effects of pesticide exposure on solitary bees

“…Sublethal effects of single compound insecticide exposure on foraging activity [ 57 , 68 – 70 ], flight [ 57 , 71 – 74 ], and food consumption by adults [ 75 – 77 ] have received some research attention. Investigations focusing on aspects of nesting activity including the number of nesting bees [ 60 , 78 ], number of brood cells produced [ 51 , 52 , 57 , 60 , 62 , 69 , 74 , 78 – 80 ], number of nests/female [ 45 , 57 , 70 ], and the number of days spent nesting have been published. The effects of exposure to pesticide mixtures on foraging activity [ 55 , 68 – 70 , 81 ], flight [ 71 , 73 , 81 ], food consumption by adults [ 75 , 76 , 82 ] and nesting [ 55 , 68 – 71 , 73 , 81 , 83 , 84 ] have also been investigated.…”

“…Larvae are the most frequently evaluated developmental stage and include assessments of the number of cocoons [ 53 , 57 , 78 ], time to cocoon completion [ 54 , 61 , 74 , 85 ] and cocoon darkening [ 54 ], and food conversion [ 56 , 85 , 86 ]. Pesticide effects on emergence and eclosion are also commonly studied with an emphasis on emergence success [ 52 , 57 , 61 , 62 , 70 , 74 , 80 , 85 , 86 ] and time to emergence [ 54 , 58 , 87 ]. Effects of pesticide exposure on offspring size [ 52 , 54 , 56 – 58 , 61 , 78 , 80 ] and sex ratio [ 52 , 57 , 59 – 61 , 70 , 78 , 80 , 85 , 87 ] have also received some research attention.…”

“…Pesticide effects on emergence and eclosion are also commonly studied with an emphasis on emergence success [ 52 , 57 , 61 , 62 , 70 , 74 , 80 , 85 , 86 ] and time to emergence [ 54 , 58 , 87 ]. Effects of pesticide exposure on offspring size [ 52 , 54 , 56 – 58 , 61 , 78 , 80 ] and sex ratio [ 52 , 57 , 59 – 61 , 70 , 78 , 80 , 85 , 87 ] have also received some research attention. Only four publications investigated the effects of pesticide mixtures on the number of eggs and larvae, larval mortality, overwintering survival and sex ratio [ 55 , 70 , 73 , 81 , 88 ].…”

“…Foraging and nesting activity. Sublethal effects of single compound insecticide exposure on foraging activity [57,[68][69][70], flight [57,[71][72][73][74], and food consumption by adults [75][76][77] have received some research attention. Investigations focusing on aspects of nesting activity including the number of nesting bees [60,78], number of brood cells produced [51,52,57,60,62,69,74,[78][79][80], number of nests/female [45,57,70], and the number of days spent nesting have been published.…”

“…Investigations focusing on aspects of nesting activity including the number of nesting bees [60,78], number of brood cells produced [51,52,57,60,62,69,74,[78][79][80], number of nests/female [45,57,70], and the number of days spent nesting have been published. The effects of exposure to pesticide mixtures on foraging activity [55,[68][69][70]81], flight [71,73,81], food consumption by adults [75,76,82] and nesting [55, 68-71, 73, PLOS ONE 81,83,84] have also been investigated. Generally, effects observed depend on the pesticide(s) studied, and, since there are limited investigations, clear trends are difficult to establish.…”